Tobacco smoke filter element and method for making

ABSTRACT

Tobacco smoke filter element comprising a porous filter body having an outer wall surface and two end wall surfaces and being adapted to be provided with an overwrap. The porous filter body is provided with two elongated chambers, each chamber being enclosed along its length by the porous filter body and extending from the surface of the outer wall into the filter body and through the surface of an end wall different from that end wall surface through which the other elongated chamber extends, thereby resulting in smoke flow patterns which cause the smoke particles to flow both axially and traversely through the filter body; and the method for forming the elongated chambers in the filter element.

United States Patent Dixon 51 July 25, 1972 TOBACCO SMOKE FILTER ELEMENT AND METHOD FOR MAKING lnventor: Ronald L. Dixon, Kingsport, Tenn.

Assignee: Eastman Kodak Company, Rochester,

April 5, 1971 Filed:

Appl. No.:

US. Cl 131/261 B, 83/30, 83/660, 131/10 A Int. Cl ..A24d 01/04, A24f 07/04, A24f 13/06 FieldofSearch ..l3l/lO.5,26l B, 10A, 10 R, 131/103, 15 B, 4 B, 253; 83/30, 660, 39, 50

References Cited UNITED STATES PATENTS 3/1964 Bartolomeo 131/253 11/1960 Bartolomeo ..l3l/l0 A X 7/1962 Bartolomeo ..l3l/10.5 X 2/1969 Kandel .;13l/l0.5 X

FOREIGN PATENTS OR APPLICATIONS 561,979 ll/1957 Belgium ..l3l/26l B Primary Examiner-Samuel Koren Assistant Examiner.l. F. Pitrelli Anorney-Cecil D. Quillen, Jr. and Malcolm G. Dunn [57] ABSTRACT Tobacco smoke filter element comprising a porous filter body having an outer wall surface and two end wall surfaces and being adapted to be provided with an overwrap. The porous filter body is provided with two elongated chambers, each chamber being enclosed along its length by the porous filter body and extending from the surface of the outer wall into the filter body and through the surface of an end wall different from that end wall surface through which the other elongated chamber extends, thereby resulting in smoke flow patterns which cause the smoke particles to flow both axially and traversely through the filter body; and the method for forming the elongated chambers in the filter element.

1 1 Claims, 4 Drawing Figures Patented July 25, 1972 3,678,941

42 2 4 f x r RONALD LDIX INVEN BY TH ATTORNEY TOBACCO SMOKE FILTER ELEMENT AND METHOD FOR MAKING BACKGROUND OF THE INVENTION This invention relates to an improved filtering device particularly adapted for use as a tobacco smoke filter.

A most important purpose of a tobacco smoke filter is to reduce the delivery of tar," which is properly called the total particulate matter (TPM) in the smoke. Another purpose of a tobacco smoke filter is to alter the composition of the smoke in a desired way such as the removal of certain compounds found in the vapor phase of tobacco smoke.

To accomplish these ends, many kinds of cigarette filters have been devised. Paper, cotton and cellulose acetate fibers have been used, and more complicated configurations involving separate sections of cellulose acetate fiber with activated charcoal, or sections of paper and cellulose acetate fiber have been used. In most of these cigarette filters, the filter element is substantially the same diameter as the tobacco part of the cigarette, and varies from about to about 25 mm. in length. The composition and structure of these filters is substantially uniform everywhere in the transverse cross-section. The tobacco smoke traverses the filter from one end to the other in a manner we shalldescribe as axial How.

The pressure drop through this filter is determined by the material of construction, the packing density, the length and the diameter. The diameter, being nearly the same for all cigarette filters, is not an important variable for use in affecting filtration. The habits and taste of cigarette smokers have demanded that the pressure drop through a cigarette not exceed about three inches of water, at a standard flow rate of 35 ml. per two seconds of flow. With a given material and a given construction of a cigarette filter, the ability of the filter to remove TPM can be altered by changing the packing density, fineness of fiber, etc. However, the higher the TPM removal, the higher the pressure drop.

It is known that a filter of sufficiently large face area can remove substantially all of the TPM with acceptable pressure drop. An example of such a filter is the Cambridge filter; this filter in the axial-flow design is impractical because the required face area is intolerably large. That is, the required area is much greater than that of the transverse cross section of a cigarette.

Large bundles of crimped textile fibers, known in the trade as tows, have been used extensively for the manufacture of cigarette filters. The vast majority of cigarette filters currently made in the United States are manufactured from such tows. Among the properties of textile tows that make them desirable for this use are: (1) they can be processed into filters continuously at very high manufacturing speeds; (2) filters made from the tows are fairly effective for trapping nicotine and tar, and (3) by proper selection of fibers and fiber modifications it is possible to selectively remove certain components from smoke.

Tobacco smoke filters of this invention are characterized by I a filtration coefficient of about 0.25 or higher as calculated by the following equation:( *John E. Kiefer and George P. Touey in Tobacco and Tobacco Smoke" Chapter X, E. L. Wynder and D. I-Iofi'man, Academic Press, New York 1967)).

where R represents the fraction of tar or nicotine captured by the filters; Ap is the pressure difierential across the filter and k is a constant related to the filter medium. The value of k (designated filtration coefficient) for conventional filters made from textile tows is between 0.13 and 0.22 depending on the size and type of fibers (assuming Ap is expressed in inches of water at an air flow rate of 17.5 ml./sec.).

The mechanism of filtration that results in the unexpected high efficiency of this type filter is not completely understood; however, there are certain aspects of this mechanism which are known to me. The efficiency of a conventional fibrous filter is related to the surface area of the fibers and the linear velocity of the smoke. The pressure drop is related to the same parameters, but by a different relationship. The present invention utilizes these parameters in a manner that results in higher efficiency and lower pressure drop than does the construction used in conventional filters.

When the surface area of a conventional filter is increased substantially by adding more fibers, the pressure drop of the filter is increased beyond the practical limit. I have found a means of increasing the surface area without an undesirable high pressure drop. This objective is accomplished by a physical configuration of fibers which results in a unique flow pattern within the filter.

For example, a typical fibrous filter with a surface area of 275 cm. has a pressure drop of about 2.8 in. and a filtration efficiency of about 46 percent. If the surface area of this filter is increased to about 500 cm. by adding more fibers, the efficiency of the filter is increased to about 66 percent, but the pressure drop is increased to about 7.5 in. The same high pressure drop filter when modified according to my invention has approximately 2.5 inches of water pressure drop and 62 percent TPM removal filtration efficiency.

SUMMARY OF THE INVENTION The filter element of this invention therefore is adapted to be used with an outer wrap and comprises a porous filter body that defines first and second elongated chambers fonned within the filter body. The filter body is provided with an outer wall and two end walls. Each elongated chamber is enclosed along its length by the porous filter body and extends from the surface of the outer wall into the filter body and through the surface of an end wall different from that through which the other elongated chamber extends. The two elongated chambers within the filter body are arranged so that upon drawing smoke into the filter element a pressure differential is created between the first elongated chamber and the second elongated chamber so as to cause a portion of the smoke to flow generally transversely through the filter element from the area of one chamber toward the area of the other chamber.

The invention is further directed to the method for forming the elongated chambers in the filter element.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view in cross-section of the tobacco smoke filter element and illustrating two parallel elongated chambers formed within the body of the filter element; I

FIG. 2 is an end view of the filter element shown in FIG. I illustrating the opening of one of the elongated chambers being approximately concentric with the longitudinal axis of the filter element;

FIG. 3 is an elevational view in cross-section illustrating a tobacco smoke filter rod of indefinite length positioned within a tubular member, and further illustrating members that may be used to pierce the filter rod as the piercing members pass through guide apertures in the tubular member; and

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3.

This invention will be described by referring to cigarette filters made from a textile tow, the textile tow being made from thermoplastic fibers such as polyolefin, polyester, cellulose ester and biphase fiber. The filter may be formed from a crimped textile tow by methods known in the art. The filter may also be made from paper, as will also be described by examples given herein. It is to be understood that the filter may be made from any known filter material which can be shaped.

Referring now to the drawings, the filter element illustrated is made from a filter material that has been formed into a cylindrical rod or filter body that is processed through an apparatus that forms the elongated chambers, the cylindrical rod subsequently being cut at predetemiined spaced intervals to form tobacco smoke filter elements of desired lengths. It is to be understood that each filter element or body in use will be provided with an outer wrap to enclose the outer wall surface of the filter body, thereby closing off the openings in the outer wall where the elongated chambers extend through the outer wall surface. For ease of description, the outer wrap will not be referred to other than a brief mention of its location in the drawings.

The tobacco smoke filter element comprises a porous filter body 12 which is adapted to be used with an outer wrap 14. As stated above, the material 16 of the porous filter body may be a crimped textile tow, paper or any other known filter material which can be readily shaped into any desired configuration.

The porous filter body 12 has an outer wall 18 that defines the outer circumference of the filter, body and which lies within the outer wrap 14 that is shown in FIG. 1, for instance, and has two end walls 20, 22. The porous filter body further defines two elongated chambers 24, 26 that are formed within the filter body and thus are enclosed along their length by the porous filter body. The elongated chambers are slanted at an angle with respect to the longitudinal axis of the filter body and in such manner so that each elongated chamber extends from the surface of the outer wall 18 into the filter body and through the surface of an end wall (either 20 or 22) difi'erent from that end wall (either 22 or 20) through which the other elongated chamber extends. Preferably, the opening through an end wall surface is approximately concentric with the longitudinal axis of the filter element or body, as shown at 28 in FIGS. 1 and 2 or at 30 in FIG. 1. The centering of this opening is thought to be more aesthetically pleasing to a person smoking a cigarette'when viewed from the visible end of the filter element as connected to a tobacco column.

The two elongated chambers 24, 26 in the filter body 12 are preferably parallel to each other, and each elongated chamber extends into the filter body from the surface of the outer wall as an opening (either 32 or 34) at a location that is offset from the location where the other elongated chamber extends into the filter body from the outer wall surface as an opening (either 34 or 32). Each opening (either 32 or 34) is also at a location that is on the opposite side of the filter body from the location where the other opening (either 34 or 32) is located.

Most commercial tobacco smoke filter elements are usually I in the range of about to 25 millimeters in length and about 7.9 millimeters in diameter. The preferred parallel distance between the two elongated chambers is about 3 to 5 millimeters. The preferred diameter of the elongated chambers is about 0.0625 to 0.080 inches.

Although the method for achieving the high TPM removal efficiency is not completely understood, it is believed to be related to the smoke flow pattern in the filter element or body. Smoke enters the filter body axially and travels through the filter body taking the path of least resistance. The smoke can directly enter the first elongated chamber 26 through opening 30, and can also enter the material of the porous filter body of the end cross-section and pass into the first elongated chamber 26, or pass on axially through the filter body depending on the resistance to the smoke flow. The resistance to the smoke flow is indicated by a pressure drop at a given flow rate. If the pressure drop across portion e is kept lower than either of the pressure drops across portion a or portion d, smoke is caused to flow transversely from the first elongated chamber 26 to the second elongated chamber 24 in an advantageous manner. When the pressure drop across portion a or portion d is smaller than the pressure drop across portion e, smoke is caused to flow axially to elongated chamber 24 across portion d or from elongated chamber 26 across portion a in an axial manner similar to conventional filters. The elongated chambers 24 and 26 are large enough in diameter to have an insignificant pressure drop.

It is believed that when smoke is flowing across portion e the filtration efficiency of the filter element is increased for two reasons: l) the elongated chambers increase the face area for the smoke flow resulting in lower smoke velocity through portion e; and (2 the smoke particles travel generally transversely to the filter material or medium orientation exposing the smoke particles to a higher chance of collision with the surface area of the filter material or medium.

In FIGS. 3 and 4, a portion of an apparatus, a tobacco smoke filter rod piercing machine, is illustrated to show how the elongated chambers may be formed in a conventional tobacco smoke filter rod. As is well known in the art, the filter material or medium passes through a plug making machine (not shown) to be made into tobacco smoke filter rods. Some filter rods may be of such length that several filter elements may be cut or severed from a filter rod when in a cigarette making machine (not shown) where the filter element is joined in a known manner to a tobacco column to form a cigarette.

The portion of the apparatus illustrated in FIGS. 3 and 4 could be attached either to the end of such plug making machine or at the beginning of such cigarette making machine, or could be a part of a separate apparatus as an intermediate step to both machines.

A tubular member 36 is shown in part in which a filter rod 38 is positioned. The filter rod may or may not have an outer wrap 40, as the case may be. The tubular member is provided with a series of spaced guide apertures 42 which serve to guide piercing members 44 that may be reciprocally operated to pass into and through the tubular member to form the elongated chambers 43 within the filter body. The spaced guide apertures 42 are located at predetermined spaced intervals along the-tubular member. Thus when the tobacco smoke filter rod 38 is subsequently cut or severed into a plurality of tobacco smoke filter elements 10, the location of such severing as indicated by the dotted line at 46, is in such manner that each of the filter elements will have a pair of opposed end walls and a pair of elongated chambers with one end of each elongated chamber of the pair opening at the surface of an end wall of the filter element different from that end wall surface through which the other elongated chamber of the pair opens. The severing operation is also such that one end of each elongated chamber within the'filter element preferably will open substantially at the center of the surface of an end wall of the filter element.

The piercing members 44 may be in the form of heated solid pins of any desired configuration in crosssection, or in the form of hollow pins (not shown) with hot air flowing through the center, or in the form of hollow, porous or open holeshaped inserts (not shown) through which a solvent is injected for dissolving the filter material or medium. It is also contemplated that there may be an insert that would disappear after the plasticizer (as for a textile fibrous filter material) has firmed the filter (e.g. ice which would turn into water). The preferred embodiment and the simplest, however, would be a heated pin of any desired configuration in cross-section that would be maintained in the filter rod for a predetennined length of time sufficient to form the wall surfaces of the elongated chambers in such desired configuration.

The heated piercing member 44 or pin may be heated by any common method such as a cartridge heater element (not shown) to which the pin is attached, by retracting the pin into a heated cavity (not shown) when not in use. The pin temperatures should be high enough, as with respect to a textile tow material, to form or mold" the elongated chambers quickly but not so high as to fuse into a tobacco smoke impermeable membrane the contacted fibers of the textile tow filter medium. An acceptable upper limit of temperature would be any temperature less than the melting point of the particular filter material being used.

If an outer wrap is used on the tobacco smoke filter rod 38 as shown in FIGS. 3 and 4 at 40, the outer wrap will also be pierced, but then the ultimate outer wrap (now shown) that would be employed in the cigarette making machine when joining a tobacco column to a filter element would cover the openings that lead into the elongated chambers at the outer wall surface.

This invention will be further illustrated by the following examples of preferred embodiments although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the infilter element a pressure difi'erential is created between the first chamber and the second chamber to cause a portion of the smoke to flow generally transversely through the filter element from the area of one chamber toward the area of the A. Specifications for the filter element examples below are as follows:

(1) Filter mater al is 1.6 denier per filament, 66,000 total denier cellulose acetate tow with 6% triacetin plasticizer.

(2) 7.9 millimeters in diameter by millimeters long and having a conventional paper outer wrap.

(3) Two iia inch (.0625) diameter co-planar elongated chambers pierced on a diameter at about 13 angle to the axis of the filter element and exiting through the center of an end wall surface.

(4) Pin for pierc ng being pointed with about 19 angle tip and heated to 125-160 C- (5) Mold time (pin retention time in filter element) of about 5-10 seconds.

(6) The expression hand pierced where indicated means that the filter elements are manually pierced with a heated pin without the aid of a tubular member or guide apertures at approximately the angle indicated in (3) above. The expression machine pierccdl where indicated means that the filter elements are pierced in a piercing machine with the aid of a tubular member and guide apertures at the angle indicated in (3) above.

(7) The parallel distance between the elongated chambers is about 4 millimeters.

. Specifications for the filter element example below are the same as in A. above except that the cellulose acetate tow is 1.6 denier per filament, 76,000 total denier.

9. Hand pierced 2. 6 .60 60 36' C. Specifications for the filter clement examples below are the same as in A. above except that the filter elements are 20 millimeters long, and the elongated chambers were pierced on a diameter of about 155 angle to the axis of the filter element.

10. Hand pierced. 5 51 51 20 11. Hand pierced 2. 7 52 52 .27 12. Hand pierced 2. 7 52 52 27 13. Hand pierced 2. 5 52 52 30' 14. Hand pierced 2.8 50 25 15. Machine pierced 2. 3 51 51 31 16. Machine pierced 2. 6 51 51 .28 D. Specifications for the filter element examples below are the same as in A. above except that the filter elements are 15 millimeters long and the elongated chambers exited through the end wall surface oii center.

17. Hand pierced 2. 4 46 46 26 18. Hand pierced 2. 3 .47 47 .28 E. Specifications for the filter element examples below are the same as in A. above except that the parallel distance between the elongated chambers is about 3 millimeters and the diameter 01 the elongated chambers is 0.080 inch.

19. Machine pierced 1. 5 56 56 54 20. Machine pierced 1.7 .56 56 49 21. Machine pierced 1.8 56 56 46 F. Specifications for the filter element examples below are the same as in A. above except that the parallel distance between the elongated chambers is about 5 millimeters and the diameter of the elongated chambers is 0.080 inch.

22. Machine pierced 2.6 63 .38 23. Machine pierced 2.7 .62 62 .36

G. Specifications for the filter clement example below is the same as in A. above except that the filter material is commercial crepe paper type, and the average weight for a 78 millimeter filter rod from which the filter elements are severed is about 725.5 milligrams.

24. Machine pierced II. Specifications for the filter clcincnt example below is the same as in G that the mold time (pin retention time in thc filter element) is about 12 seconds.

25. Machine pierced 2 4 above except I. Specifications for the filter element example below is that the commercial crepe paper type filter material does not have any elongated 26. Not pierced While the invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. Tobacco smoke filter element adapted to be used with an outer wrap, said element comprising a porous filter body having an outer side wall and end walls, said porous filter body defining first and second elongated chambers, each elongated chamber being enclosed along its length by the porous filter body and extending from the surface of the side wall into the filter body and through the surface of an end wall different from that through which the other chamber extends, said chambers formed therein. 3. 66

2. A tobacco smoke filter element as defined in claim 1, and wherein the two elongated chambers are parallel to each other.

3. A tobacco smoke filter element as defined in claim 1, and wherein each elongated chamber extends into the filter body through the surface of an end wall as an opening approximately concentric with the longitudinal axis of the filter element.

4. A tobacco smoke filter element as defined in claim 1, and wherein each elongated chamber extends into the filter body from the surface of the side wall as an opening at a location that is offset from the location where the other elongated chamber extends into the filter body from the side wall surface as an opening.

5. Tobacco smoke filter element as defined in claim 1, and

chambers being arranged so that upon drawing smoke into the wherein each elongated chamber extends into the filter body from the surface of said side wall as an opening at a location that is on the opposite side of said filter body from the location where the other elongated chamber extends into the filter body from the side wall surface as an opening.

6. Tobacco smoke filter element as defined in claim 2, and wherein said filter element is about to millimeters in length and about 7.9 millimeters in diameter, and the parallel distance between the two elongated chambers is about 3 to 5 millimeters with each chamber being about 00625 to 0.080 inches in diameter.

7. The method of forming a tobacco smoke filter element having a porous filter body provided with an outer side wall and end walls by forming in the filter body two elongated chambers, each elongated chamber being enclosed along its length by the porous filter body and extending from the surface of the side wall into the filter body and through the surface of an end wall different from that through which the other tinuous filter body for a predetermined length of time suffcient to form the wall surfaces of said chambers in a desired configuration in cross-section.

10. The method of forming a tobacco smoke filter element from a tobacco smoke filter rod having a porous filter body and provided with an outer wall surface, said method comprising the steps of piercing the outer wall surface of the filter rod from one side of the filter rod through the opposite side at predetermined spaced intervals along the length of the filter rod to form elongated chambers that are slanted at an angle with respect to the longitudinal axis of the filter rod; and

severing the filter rod transversely into a plurality of said filter elements in such manner and at such locations that each of the filter elements will have a pair of opposed end walls and a pair of elongated chambers with one end of each elongated chamber of the pair opening at the surface of an end wall of the filter element different from that end wall surface through which the other elongated chamber of the pair opens.

l l. A method as defined in claim 10 and wherein said filter rod is severed at such locations along the length of the filter rod that one end of each elongated chamber within a filter element opens substantially at the center of the surface of an end wall of the filter element. 

1. Tobacco smoke filter element adapted to be used with an outer wrap, said element comprising a porous filter body having an outer side wall and end walls, said porous filter body defining first and second elongated chambers, each elongated chamber being enclosed along its length by the porous filter body and extending from the surface of the side wall into the filter body and through the surface of an end wall different from that through which the other chamber extends, said chambers being arranged so that upon drawing smoke into the filter element a pressure differential is created between the first chamber and the second chamber to cause a portion of the smoke to flow generally transversely through the filter element from the area of one chamber toward the area of the other chamber.
 2. A tobacco smoke filter element as defined in claim 1, and wherein the two elongated chambers are parallel to each other.
 3. A tobacco smoke filter element as defined in claim 1, and wherein each elongated chamber extends into the filter body through the surface of an end wall as an opening approximately concentric with the longitudinal axis of the filter element.
 4. A tobacco smoke filter element as defined in claim 1, and wherein each elongated chamber extends into the filter Body from the surface of the side wall as an opening at a location that is offset from the location where the other elongated chamber extends into the filter body from the side wall surface as an opening.
 5. Tobacco smoke filter element as defined in claim 1, and wherein each elongated chamber extends into the filter body from the surface of said side wall as an opening at a location that is on the opposite side of said filter body from the location where the other elongated chamber extends into the filter body from the side wall surface as an opening.
 6. Tobacco smoke filter element as defined in claim 2, and wherein said filter element is about 15 to 25 millimeters in length and about 7.9 millimeters in diameter, and the parallel distance between the two elongated chambers is about 3 to 5 millimeters with each chamber being about 0.0625 to 0.080 inches in diameter.
 7. The method of forming a tobacco smoke filter element having a porous filter body provided with an outer side wall and end walls by forming in the filter body two elongated chambers, each elongated chamber being enclosed along its length by the porous filter body and extending from the surface of the side wall into the filter body and through the surface of an end wall different from that through which the other chamber extends.
 8. The method as defined in claim 7, and wherein the elongated chambers are formed by elongated members that pierce the side wall of a continuous, porous filter body and extend through the continuous filter body to and through the opposite side of the continuous filter body, and wherein said continuous filter body is severed transversely to form the first mentioned filter body.
 9. The method as defined in claim 8, and wherein the elongated members are heated pins and are maintained in the continuous filter body for a predetermined length of time sufficient to form the wall surfaces of said chambers in a desired configuration in cross-section.
 10. The method of forming a tobacco smoke filter element from a tobacco smoke filter rod having a porous filter body and provided with an outer wall surface, said method comprising the steps of piercing the outer wall surface of the filter rod from one side of the filter rod through the opposite side at predetermined spaced intervals along the length of the filter rod to form elongated chambers that are slanted at an angle with respect to the longitudinal axis of the filter rod; and severing the filter rod transversely into a plurality of said filter elements in such manner and at such locations that each of the filter elements will have a pair of opposed end walls and a pair of elongated chambers with one end of each elongated chamber of the pair opening at the surface of an end wall of the filter element different from that end wall surface through which the other elongated chamber of the pair opens.
 11. A method as defined in claim 10 and wherein said filter rod is severed at such locations along the length of the filter rod that one end of each elongated chamber within a filter element opens substantially at the center of the surface of an end wall of the filter element. 